I'll quote the subheading and a couple of paragraphs and leave it up to my readers to discuss. Is this a good example of how scientists should explain evolutionary biology to the general public?

The only unproven area is Darwin's natural selection

...

Living organisms, on the other hand, evolve by variational evolution that depends on the survival and reproduction of the "fittest" individuals in the population, which is composed of many genotypes.

Unlike evolution, which is taken as a fact, the theory of natural selection, Darwin's mechanism for evolution, has come under criticism as to whether it is sufficient to explain evolution. In particular, early developmental biologists questioned if natural selection was adequate to explain the diversity and complexity of life.

Yet after 150 years of vigorous research (and many Nobel prizes!), no one has come up with a better theory. In fact, the more scientists have explored biology, the more they have become convinced of the facts of evolution.

Natural selection is a fact of everyday life. Resources are limited, individuals differ in their survival and reproduction, and evolution is a common sense conclusion deduced from facts and reasons. The problem with evolutionary change is that it takes place on such a slow place that we do not see it. However, we can imagine how evolution occurs by looking at the spectacular variety of food plants, flowers and domestic animals that we have produced by using the same principles of genetics and selection that nature uses. We may not witness the origin of species, but we have witnessed species becoming extinct in our own life time.

I'll get the conversation going by pointing out that well before the 150 years Professor Singh mentions in his article, random genetic drift was proposed as a pretty good theory about how evolution can occur. It may not be "better" than natural selection but I think it's good enough to have deserved a mention.

14 comments
:

Doesn't the existence of evolutionary stasis (including "living fossils") prove that drift - especially drift in genes related to phenotypically variation - is generally not all that important? If drift (as well as selectively neutral phenotypic variation, which you link to drift) was as important as you say, wouldn't all species morphologically "drift" all over the place rather than displaying statis for millions and tens of millions of years? I know, you'll protest that drift only is a factor in small populations. Then explain the living fossil, the coelacanth. The fact is that the common phenomenon of stasis is a sure sign of stabilizing selection. Admittedly, drift sometimes matters - usually in boring, nonconsequential, phenotypically invisible genetic variation.

There are aspects of the article that we felt would be received poorly - He's already caught flak for using the analogy of automobiles (OMG they're designed!!!!).

As a post-doc of R.C. Lewontin, my supervisor as much as anyone, is not an adaptationist. Our lab does a lot of speciation work, and we're already bristling at the recent Scientific American 'allegation' that neutral evolution has been somehow ruled out of speciation.

I know that Dr. Singh has written several articles in the Hamilton Spectator over the years, and I've been surprised at how detailed some of them are (he had a rather in depth article about human genetic variation in 2002). I'm not sure that this would have been the best forum for bringing in random genetic drift, though I'm sure that there could've been a way to do it. I'm just more impressed that he takes the time out of his work to write this kind of stuff because not every scientist does.

I'm not sure that this would have been the best forum for bringing in random genetic drift, though I'm sure that there could've been a way to do it.

Of course there was a way to do it.

Here's what Rama said,

Unlike evolution, which is taken as a fact, the theory of natural selection, Darwin's mechanism for evolution, has come under criticism as to whether it is sufficient to explain evolution. In particular, early developmental biologists questioned if natural selection was adequate to explain the diversity and complexity of life.

Yet after 150 years of vigorous research (and many Nobel prizes!), no one has come up with a better theory.

I would have replaced the last sentence with.

Today, 150 years after the publication of "On the Origin of Species," we know that natural selection is not the only mechanism of evolution. Much of the diversity we see around us can easily be explained by accidental evolution—the mechanism is called random genetic drift and it is the opposite of adaptive natural selection.

Natural selection is still the only known mechanism when it comes to explaining adaptations. Darwin was 100% correct about that.

Furthermore, the fact of evolution—that life has evolved over billions of years from a single common ancestor (or a small number of common ancestors)—has been so overwhelmingly verified by additional evidence that it is now considered a fact and not a theory.

How hard is that? My version has the disadvantage of being slightly more complicated but it has the advantage of being a lot more correct.

When it comes to writing for the general public, the debate is over "dumbing down" versus "accurate." I always come down on the side of "accurate." How about you?

When it comes to writing for the general public, the debate is over "dumbing down" versus "accurate." I always come down on the side of "accurate." How about you?

You'll find no disagreement from me. I've read enough Gould to think that there's a proper way to convey complex concepts. Even if the public fails to understand it, scientists retain the ethical 'high-ground'.

However, now I'm caught in the awkward position of agreeing with you that my supervisor could have done a better job ;-)

"Yet after 150 years of vigorous research (and many Nobel prizes!), no one has come up with a better theory"

I don't see anything wrong with this general statement. He probably should have stated random drift as another mechanism, but it's not a "better" one. I think for the layman this is not too bad. The way I see it, a layman can understand evolution quite well without knowing about random drift. As for the debate between "dumbing down" and being accurate, I too don't think it should be an either/or question. On the other hand, it is quite difficult to achieve flawless accuracy and yet retain clarity, simplicity and accessibility; very few people can do this. Maybe you can write an evolution book for laymen and demonstrate how it can be done.

Larry: Much of the diversity we see around us can easily be explained by accidental evolution—the mechanism is called random genetic drift and it is the opposite of adaptive natural selection.

There are a lot of terms in this passage that are ill defined. In particular I really don’t understand what you mean by saying drift is the opposite of NS. Since you say “diversity we see around us” I take that to mean you are referring to phenotypically visible differences.

It is one thing to say that a particular mechanism can account for some difference, it is another to prove it. NS can "explain" every phenotypically visible difference between two species at least as easily as (and often better than) random drift can, but until one has gone beyond the principle of the process and prove that *that* mechanism was the one responsible, it remains a conjecture (drift *or* NS). And with respect to phenotypically visible differences, NS often has the more plausible argument.

Since both NS and drift occur via the same basic process, it can be very hard to distinguish them. (Drift is the change in allele frequency in successive generations due to random chance only, whereas NS is the *same thing* except one allele has a probabilistic advantage.) Even where one tracks allele frequency over hundreds of generations (in a constant environment!), unless a particular allele gives an enormous advantage, evidence for NS from just that data would not be clear. But that would be no evidence that it was purely drift.

And thus I am reminded to be careful of what I blog about when I'm signing my name to it...

Do you know that Rama and I had a joint NSERC grant back in 1982-84?

Actually, I did! A few months ago I mentioned to him that I'd read an interesting post on your blog; to which Rama replied that he knew you and that you'd previously collaborated in looking into the evolutionary dynamics of heat-shock proteins (I didn't get any details). Not sure if he actually ever reads the blogosphere though, I should send him a few links.

Larry said: "Next time you're out on the street look at the people around you. You will see tons of phenotypic differences that have an underlying genetic component. This is what diversity is all about. What percentage do you think is in the process of being fixed by natural selection?"

The US is an ethnically diverse country with people just a few generations removed from ethnically uniform populations from all corners of the world. I can think of plausible explanations for differences in outward appearance (shape/color of eyes, hair type/color, shape of nose and cheeks, butt size, etc) in the source populations, mostly related to sexual selection of appearance (to a standard that is local and can "drift" in the sense that it is arbitrary and dependent on what the mean of the population is, but selected nonetheless).

I can prove none of that for any particular feature, but there is lots of evidence to suggest that animals (including humans) have such mating preferences (e.g., subspecies/varieties prefer to mate within their group when given a choice). So anything that affect outward appears I would presume is likely to be (or at least was before modern times) something that was the focus of sexual selection.

OTOH, your job is tougher. To credibly claim it is drift you have to rule out selection at any time from the moment the different allele appeared until it became fixed in the source population.

Have you, or anyone, done this for any allele that underlies any of this "diversity" you speak of?

If not, what is the basis for your presumption that "much" of it is due to drift? You are the one making the claim. Back it up with reasons and/or evidence.

"Doesn't the existence of evolutionary stasis (including "living fossils") prove that drift - especially drift in genes related to phenotypic variation - is generally not all that important?"

Nice argument, but stasis does not mean that speciation by cladogenesis is not going on. To fail to observe stasis you would need all populations of the ancestral species replaced or wiped out. According to Niles Eldredge, that is not so easy. The average species lasts millions of years.This relates to the topic of geographic isolation...bottlenecks, foundation effects...

The "coelocanth" Latimeria is a living representative of the coelocanthiformes but the genus is only known from extant species (there are several other, fossil genera of Latimeriidae). There has been evolution going on there, you know.

I can prove none of that for any particular feature, but there is lots of evidence to suggest that animals (including humans) have such mating preferences (e.g., subspecies/varieties prefer to mate within their group when given a choice). So anything that affect outward appears I would presume is likely to be (or at least was before modern times) something that was the focus of sexual selection.

Sh*t. I should have remembered the "sexual selection" argument. It's proven to be a great boon for all adaptationists. They can avoid having to think about their bias by falling back on the good-old "sexual selection" argument.

Let's change the question to maple trees. Look at all the phenotypic variation within a species of maple tree and between closely related species.

Do you think it's all due to adaptation?

OTOH, your job is tougher. To credibly claim it is drift you have to rule out selection at any time from the moment the different allele appeared until it became fixed in the source population.

Strictly speaking, you are correct if I'm required to "prove" that an allele frequency is changing by drift and not selection. But let's not forget that drift is the default hypothesis. If there's no evidence of selection then drift is the most likely explanation.

Have you, or anyone, done this for any allele that underlies any of this "diversity" you speak of?

Most haven't been looked at. If there was selection against certain phenotypes in favor of others (e.g. size of your feet, male pattern baldness, ability to roll your tongue, length of your fingers, shape of your nose, dry ear wax) then we would expect that the alleles would be eliminated quite quickly.

The fact that they have persisted strongly suggests that they are neutral. Indeed, the overall prevalence of phenotypic variation within a population is more consistent with drift than adaptation.

If not, what is the basis for your presumption that "much" of it is due to drift?

Because it's the default explanation. The onus is on the adaptationists to show that most of the phenotypic variation is adaptive.

Heck, they don't even need to prove it. All they have to do is offer reasonable explanations when asked to defend their bias. (Sexual selection isn't a reasonable explanation for most species.)

You are the one making the claim. Back it up with reasons and/or evidence.

Sorry, it doesn't work like that. If you make the positive claim that something is adaptive (or deleterious) then it's up to you to back it up. In the absence of evidence we assume that the allele confers no particular advantage or disadvantage.

Laurence A. Moran

Larry Moran is a Professor in the Department of Biochemistry at the University of Toronto. You can contact him by looking up his email address on the University of Toronto website.

Sandwalk

The Sandwalk is the path behind the home of Charles Darwin where he used to walk every day, thinking about science. You can see the path in the woods in the upper left-hand corner of this image.

Disclaimer

Some readers of this blog may be under the impression that my personal opinions represent the official position of Canada, the Province of Ontario, the City of Toronto, the University of Toronto, the Faculty of Medicine, or the Department of Biochemistry. All of these institutions, plus every single one of my colleagues, students, friends, and relatives, want you to know that I do not speak for them. You should also know that they don't speak for me.

Subscribe to Sandwalk

Quotations

The old argument of design in nature, as given by Paley, which formerly seemed to me to be so conclusive, fails, now that the law of natural selection has been discovered. We can no longer argue that, for instance, the beautiful hinge of a bivalve shell must have been made by an intelligent being, like the hinge of a door by man. There seems to be no more design in the variability of organic beings and in the action of natural selection, than in the course which the wind blows.Charles Darwin (c1880)Although I am fully convinced of the truth of the views given in this volume, I by no means expect to convince experienced naturalists whose minds are stocked with a multitude of facts all viewed, during a long course of years, from a point of view directly opposite to mine. It is so easy to hide our ignorance under such expressions as "plan of creation," "unity of design," etc., and to think that we give an explanation when we only restate a fact. Any one whose disposition leads him to attach more weight to unexplained difficulties than to the explanation of a certain number of facts will certainly reject the theory.

Charles Darwin (1859)Science reveals where religion conceals. Where religion purports to explain, it actually resorts to tautology. To assert that "God did it" is no more than an admission of ignorance dressed deceitfully as an explanation...

Quotations

The world is not inhabited exclusively by fools, and when a subject arouses intense interest, as this one has, something other than semantics is usually at stake.
Stephen Jay Gould (1982)
I have championed contingency, and will continue to do so, because its large realm and legitimate claims have been so poorly attended by evolutionary scientists who cannot discern the beat of this different drummer while their brains and ears remain tuned to only the sounds of general theory.
Stephen Jay Gould (2002) p.1339
The essence of Darwinism lies in its claim that natural selection creates the fit. Variation is ubiquitous and random in direction. It supplies raw material only. Natural selection directs the course of evolutionary change.
Stephen Jay Gould (1977)
Rudyard Kipling asked how the leopard got its spots, the rhino its wrinkled skin. He called his answers "just-so stories." When evolutionists try to explain form and behavior, they also tell just-so stories—and the agent is natural selection. Virtuosity in invention replaces testability as the criterion for acceptance.
Stephen Jay Gould (1980)
Since 'change of gene frequencies in populations' is the 'official' definition of evolution, randomness has transgressed Darwin's border and asserted itself as an agent of evolutionary change.
Stephen Jay Gould (1983) p.335
The first commandment for all versions of NOMA might be summarized by stating: "Thou shalt not mix the magisteria by claiming that God directly ordains important events in the history of nature by special interference knowable only through revelation and not accessible to science." In common parlance, we refer to such special interference as "miracle"—operationally defined as a unique and temporary suspension of natural law to reorder the facts of nature by divine fiat.
Stephen Jay Gould (1999) p.84

Quotations

My own view is that conclusions about the evolution of human behavior should be based on research at least as rigorous as that used in studying nonhuman animals. And if you read the animal behavior journals, you'll see that this requirement sets the bar pretty high, so that many assertions about evolutionary psychology sink without a trace.

Jerry Coyne
Why Evolution Is TrueI once made the remark that two things disappeared in 1990: one was communism, the other was biochemistry and that only one of them should be allowed to come back.

Sydney Brenner
TIBS Dec. 2000
It is naïve to think that if a species' environment changes the species must adapt or else become extinct.... Just as a changed environment need not set in motion selection for new adaptations, new adaptations may evolve in an unchanging environment if new mutations arise that are superior to any pre-existing variations

Douglas Futuyma
One of the most frightening things in the Western world, and in this country in particular, is the number of people who believe in things that are scientifically false. If someone tells me that the earth is less than 10,000 years old, in my opinion he should see a psychiatrist.

Francis Crick
There will be no difficulty in computers being adapted to biology. There will be luddites. But they will be buried.

Sydney Brenner
An atheist before Darwin could have said, following Hume: 'I have no explanation for complex biological design. All I know is that God isn't a good explanation, so we must wait and hope that somebody comes up with a better one.' I can't help feeling that such a position, though logically sound, would have left one feeling pretty unsatisfied, and that although atheism might have been logically tenable before Darwin, Darwin made it possible to be an intellectually fulfilled atheist

Richard Dawkins
Another curious aspect of the theory of evolution is that everybody thinks he understand it. I mean philosophers, social scientists, and so on. While in fact very few people understand it, actually as it stands, even as it stood when Darwin expressed it, and even less as we now may be able to understand it in biology.

Jacques Monod
The false view of evolution as a process of global optimizing has been applied literally by engineers who, taken in by a mistaken metaphor, have attempted to find globally optimal solutions to design problems by writing programs that model evolution by natural selection.